DEM analysis of the sand plug behavior during the installation process of open-ended pile

Abstract

A DEM simulation of the installation process of open-ended pile is conducted by means of the particle flow code PFC 2D. Focus is placed on the investigation of the soil plug behavior, from both macroscopic and microscopic perspectives. A soil assembly with natural initial stress state is first generated and the validity of the numerical installation process is further checked. Afterwards, a macroscopic analysis is performed based on the porosity and stress state. Numerical results indicate that a dense zone, with the length about half the pile diameter, has formed at the pile tip. A dramatic load transfer is observed at the bottom of the soil plug, where the lateral pressure coefficient peaks at around 2.4. From a microscopic perspective, two modes of soil layer deflection exist for soil mass inside and under the pile, respectively. Different particle displacement patterns indicate that with increasing penetration depth and resistance accumulation, soil mass flows into the pile with a lower rate. Further analysis based on the distribution of contact force chain and principal stress rotation show that soil particles, when subjected to external disturbance, tend to rearrange to the most stable structure, which is in the arch shape. Finally, an improved arch model based on the numerical results is proposed to facilitate the understanding of the plug behavior.